Physical properties of soil

Question 1

Composition of soil

Answer 1

45% mineral matter, 25% air , 25% water , 5% organic matter

Question 2

Soil texture

Answer 2

A measure of the proportion of different sized mineral particles (sand, silt & clay) that are found in a sample

Question 3

Loam soil

Answer 3

Soil that contains equal amount of sand, silt and clay.
- Influences the aeration, drainage, available water and nutrients

Question 4

Porosity

Answer 4

TOTAL VOLUME OF SOIL OCCUPIED BY PORES.
Describes materials that contain tiny holes or pores that allow gases and liquids to pass through the material.

Question 5

Soil Triangle

Answer 5

Is used to classify a soil sample by the proportions of sand, silt and clay it
contains.

Question 6

Soil structure

Answer 6

Describes the arrangement of soil particles within a soil.

Question 7

Aggregate

Answer 7

A substance formed by combining several separate elements. Sand, silt and
clay particles cluster together.

Question 8

Cementation

Answer 8

The binding together of soil particles.

Question 9

Separation

Answer 9

Soil aggregates are broken up within the soil. Large cracks may develop in the
soil, which damages its overall structure.

Question 10

Flocculation

Answer 10

Is the clustering together of soil particles to create larger structures called
floccules.

Question 11

Plough pan

Answer 11

Layer of compaction that has been repeatedly ploughed at the same depth.
Removed using a subsoiler.

Question 12

Soil compaction

Answer 12

Occurs when soil particles are pressed together, and aggregates are destroyed.
This reduces the total pore space in the soil.

Question 13

Hygroscopic water
(absorbed water)

Answer 13

Forms a thin film around a soil particle and is held on the surface of the particle by the force of attraction.
It cannot be removed from the soil and is
not available to plants.

Question 14

Capillary water

Answer 14

Water that moves up through the soil by capillary action. Water held in smaller pores is unavailable, water held in larger pores is available to plants

Question 15

Gravitational water

Answer 15

Water that moves down through the soil pores with gravity. Temporarily available to plants before draining away.

Question 16

Field capacity

Answer 16

Is the amount of water in a soil after the gravitational water has drained away.

Question 17

Permanent wilting point

Answer 17

The point at which no more capillary water can be removed from a soil (by plant roots)

Question 18

Available water capacity

Answer 18

The amount of water between the field capacity and permanent wilting point that is available for absorption by plant roots.

Question 19

Soil colour

Answer 19

The colour of a soil can indicate its humus and mineral content.

Question 20

Soil temperature

Answer 20

The rate of a chemical reaction doubles with every 10°C rise in temperature (Van’t Hoff’s Law) so the warmer the soil, the faster the growth rate.

Question 21

Soil capping

Answer 21

A hard crust on the soil surface that limits permeability

Question 22

Carbon sequestration

Answer 22

Removal of carbon dioxide from the atmosphere by plant photosynthesis and storing as plant biomass or organic soil matter.

Question 23

Mineral matter

Answer 23

Derived from the parent material of the soil

Question 24

Organic matter

Answer 24

Contains Dead plant and animal remains ( and microbes at various stages of decomposition) which decompose to form humus which contributes to soil structure and fertility

Question 25

Cation Exchange Capacity

Answer 25

The ability of a soil to carry out cation exchange

Question 26

Sand Particles

Answer 26

• The largest particle and so the pore spaces between the particles are large.
• It’s easier to water to pass through due to large pore spaces = good drainage.
• Prone to drought during times of low rainfall
• Less prone to water logging during times of heavy rainfall.
• Air heats up faster than water, sandy soils warm up quickly.
• Sand particles do not contribute to sand fertility

Question 27

Clay Particles

Answer 27

• Clay is the smallest particle and so the pore spaces between the particles are small
• Difficult for water to pass through the soil, which means there is poor drainage.
• Less prone to drought during times of low rainfall
• Can be prone to water-logging during times of heavy rainfall.
  – Clay soils warm up slowly
• Clay particles contribute to soil fertility.

Question 28

Micro&Macro pores

Answer 28

Between the particles in aggregates are micropores,
between the aggregates are micropores

Question 29

Impact of soil structure

Answer 29

• Directly affects the movement of water and air in the soil.
• This affects the soil temperature
• The moisture, air and temperature affect the organisms in the soil e.g. plant roots and earthworms.
  Overall impact; Crop yield. Pollution. Fertiliser efficiency

Question 30

Importance of soil air

Answer 30

• Roots need to be able to respire and so need oxygen that they get from the soil air that exists in pores between particles.
• The energy from respiration is used to absorb nutrients by active transport
• When water-logging occurs, there is no air and so no oxygen present in the soil, roots cannot respire and so roots cannot absorb nutrients leading to deficiencies.
• Air improves drainage

Question 31

Moisture stress

Answer 31

Water is held tightly in soil by capillary forces

Question 32

Why a high humus content is more beneficial than a high clay content

Answer 32

Humus more fertile than clay
- Hummus holds more water
- Humus has a high CEC , which increases flocculation improving soil structure
- Humus increases earthworm activity
- Humus more beneficial more soil structure

Question 32

Why a high humus content is more beneficial than a high clay content

Answer 32

Humus more fertile than clay
- Hummus holds more water
- Humus has a high CEC , which increases flocculation improving soil structure
- Humus increases earthworm activity
- Humus more beneficial more soil structure

Question 33

Cation

Answer 33

positively charged ion

Question 34

Colloid

Answer 34

Small negatively charged particle of clay/humus

Question 35

Cation exchange

Answer 35

Swapping of positive ions on the surface of a colloid, e.g H+ changed with a Ca2+

Question 36

How is available water held in soil

Answer 36

aDsorption : held by attraction between negative charges on clay and positive charges on water molecules.

Capillary action : Water is held in small pores by capillary forces, water molecules join onto one another.

Question 37

Soil Erosion and causes

Answer 37

• The wearing away of the top layer of the soil
  Water: Impact of rain loosens the material causing small particles to separate , which are then washed away.
  Wind: Wind picks up and moves small particles from top layer of soil

Question 38

Sedimentation

Answer 38

The build up of these eroded particles in other places such as in a river

Question 39

Vegetation

Answer 39

Binds soils together and helps to prevent soil erosion and so catch crops can be used to cover otherwise fallow soil